Mimas (moon)
or | image = | caption = | orbit_ref =   | discovery = yes | discoverer = William Herschel | discovered = 17 September 1789 | periapsis = | apoapsis = | semimajor = | eccentricity = | period = | avg_speed = 14.28 km/s (calculated) | inclination = (to Saturn's equator) | satellite_of = Saturn | physical_characteristics = yes | dimensions = 415.6 × 393.4 × 381.2 km (0.0311 Earths) | mean_radius = | surface_area = – | volume = | mass =   (6.3 Earths) | density = | surface_grav = m/s2 (0.00648 g) | escape_velocity = km/s | rotation = synchronous | axial_tilt = zero | albedo = (geometric) | magnitude = 12.9  | single_temperature = ≈ 64 K }} Mimas is a moon of Saturn which was discovered in 1789 by William Herschel. It is named after Mimas, a son of Gaia in Greek mythology, and is also designated Saturn I. With a diameter of it is the smallest astronomical body that is known to be rounded in shape because of self-gravitation. Discovery Mimas was discovered by the astronomer William Herschel on 17 September 1789. He recorded his discovery as follows: "The great light of my forty-foot telescope was so useful that on the 17th of September, 1789, I remarked the seventh satellite, then situated at its greatest western elongation."Herschel, William Philosophical Transactions of the Royal Society of London, Vol. 80, reported by Name Mimas is named after one of the Giants in Greek mythology, Mimas. The names of all seven then-known satellites of Saturn, including Mimas, were suggested by William Herschel's son John in his 1847 publication Results of Astronomical Observations made at the Cape of Good Hope.As reported by William Lassell, Monthly Notices of the Royal Astronomical Society, Vol. 8, No. 3, pp. 42–43 (January 14, 1848) He named them after Titans specifically because Saturn (the Roman equivalent of Cronus in Greek mythology), was the leader of the Titans and ruler of the world for some time. The adjectival form of Mimas is Mimantean or Mimantian. The nt comes from the Latin genitive case Mimantis, from Greek Μῑμάντος; the old form of the name had been Mimans Μίμανς (Liddell and Scott's Greek-English Lexicon) Physical characteristics The surface area of Mimas is slightly less than the land area of Spain. The low density of Mimas, 1.15 g/cm³, indicates that it is composed mostly of water ice with only a small amount of rock. Due to the tidal forces acting on it, Mimas is noticeably prolate; its longest axis is about 10% longer than the shortest. The ellipsoidal shape of Mimas is especially noticeable in some recent images from the Cassini probe. Mimas's most distinctive feature is a giant impact crater across, named Herschel after the discoverer of Mimas. Herschel's diameter is almost a third of Mimas's own diameter; its walls are approximately high, parts of its floor measure deep, and its central peak rises above the crater floor. If there were a crater of an equivalent scale on Earth (in relative size) it would be over in diameter, wider than Australia. The impact that made this crater must have nearly shattered Mimas: fractures can be seen on the opposite side of Mimas that may have been created by shock waves from the impact travelling through Mimas's body. The Mimantean surface is saturated with smaller impact craters, but no others are anywhere near the size of Herschel. Although Mimas is heavily cratered, the cratering is not uniform. Most of the surface is covered with craters larger than in diameter, but in the south polar region, there are generally no craters larger than in diameter. Three types of geological features are officially recognized on Mimas: craters, chasmata (chasms) and catenae (crater chains). Orbital resonances A number of features in Saturn's rings are related to resonances with Mimas. Mimas is responsible for clearing the material from the Cassini Division, the gap between Saturn's two widest rings, the A Ring and B Ring. Particles in the Huygens Gap at the inner edge of the Cassini division are in a 2:1 resonance with Mimas. They orbit twice for each orbit of Mimas. The repeated pulls by Mimas on the Cassini division particles, always in the same direction in space, force them into new orbits outside the gap. The boundary between the C and B ring is in a 3:1 resonance with Mimas. Recently, the G Ring was found to be in a 7:6 co-rotation eccentricity resonance with Mimas; the ring's inner edge is about inside Mimas's orbit. Mimas is also in a 2:1 mean-motion resonance with the larger moon Tethys, and in a 2:3 resonance with the outer F Ring shepherd moonlet, Pandora. Exploration Pioneer 11 flew by Saturn in 1979, and its closest approach to Mimas was 104,263 km on September 1, 1979. Voyager 1 flew by in 1980, and Voyager 2 in 1981. Mimas has been imaged several times by the ''Cassini'' orbiter, which entered into orbit around Saturn in 2004. A close flyby occurred on February 13, 2010, when Cassini passed by Mimas at . In popular culture When seen from certain angles, Mimas resembles the Death Star, a fictional space station known from the 1977 film Star Wars Episode IV: A New Hope, which is said to be roughly 140 kilometres in diameter. Herschel resembles the concave disc of the Death Star's "superlaser". This is coincidental, as the film was made nearly three years before Mimas was resolved well enough to see the crater. In Star Trek: The Next Generation, Wesley Crusher once beamed to Mimas in an emergency. In 2010, NASA revealed a temperature map of Mimas, using images obtained by Cassini. The warmest regions, which are along one edge of Mimas, create a shape similar to the video game character Pac-Man, with Herschel Crater assuming the role of an "edible dot" or "power pellet" known from Pac-Man gameplay. Gallery File:Mimas before limb sharp (colored).jpg|Mimas before Saturn's limb, Feb 13, 2010 (color added to b/w original). File:CassiniPhotographMimasSaturn.jpg|Mimas is the tiny white dot in the lower left. (Click to enlarge view.) File:Mimas shape.jpg|Mimas, imaged by Cassini, looking distinctly egg-shaped. File:Mimas (NASA) PIA06176.jpg|Mimas, silhouetted against Saturn's northern latitudes. File:Mimas and F ring PIA09806.jpg|Mimas, behind the F Ring. File:Mimas limb sharp.jpg|Mimas's limb, showing striking albedo features on crater walls (Herschel is at the lower right) File:Color Near Herschel Crater.jpg|Subtle colour differences on Mimas are apparent in this false-colour view. File:Mimas PIA12569.jpg|Mimas mosaic with mostly high resolution. See also * List of natural satellites * Mimas in fiction References }} }} }} | url = http://www.sciencemag.org/content/315/5813/815.abstract| accessdate = 20 December 2011}} (supporting online material, table S1) }} External links * Cassini mission page – Mimas * Mimas Profile at NASA's Solar System Exploration site * The Planetary Society: Mimas * [http://www.nineplanets.org/mimas.html Mimas page at The Nine Planets] * Views of the Solar System – Mimas * Cassini images of Mimas * Images of Mimas at JPL's Planetary Photojournal * 3D shape model of Mimas (requires WebGL) * Paul Schenk's Mimas blog entry and movie of Mimas's rotation on YouTube * Mimas global and polar basemaps (June 2012) from Cassini images * Mimas atlas (July 2010) from Cassini images * Mimas nomenclature and Mimas map with feature names from the USGS planetary nomenclature page * Figure "J" is Mimas transiting Saturn in 1979, imaged by Pioneer 11 from here Mimas 17890917